The purpose of this project is to investigate how a neuronal network which performs a specific task clearly related to behavior is built and becomes functional during the developmental period. A network will be studied which contains many individually identified neurons and which generates a highly stereotyped motor program in an insect. Use of identified cells makes it possible to examine the topology and ultrastructure of the cell with intracellular dyes at different stages of development, and to describe how it is constructed. the stereotype of the output pattern of the adult neural network provides a precise physiological standard against which the performance of immature networks can be evaluated. An accurate characterization of functional maturation in the system can be produced by activating the network at different stages of development, either through normal sensory channels or with command interneurons. The immediate goals are to determine the timing and nature of construction of the component neurons, the timing and nature of physiological maturation of the neurons, when the neurons begin to communicate with each other to form a coordinated assembly, and whether any feedback from assembly operations is necessary to arrive at the proper adult coordination. The unusual opportunity which the study affords is that of observing how an assembly of neurons which must work together achieves functional maturity.